Exotic Populus taxa pose a threat to the success of riparian forest restoration in floodplain areas. We evaluated the impact of exotic Populus taxa on softwood riparian forest development along the river Common Meuse after introducing native Populus nigra and after the re-establishment of the natural river dynamics. We sampled 154 poplar seedlings that spontaneously colonised restored habitat and assessed their taxonomy based on diagnostic chloroplast and nuclear microsatellite markers. Furthermore, by using a paternity analysis on 72 seedlings resulting from six open pollinated Populus nigra females, we investigated natural hybridization between frequently planted cultivated poplars and native Populus nigra. The majority of the poplar seedlings from the gravel banks analyzed where identified as Populus nigra; only 2% of the sampled seedlings exhibited genes of exotic poplar species. Similarly, the majority of the seedlings from the open pollinated progenies were identified as Populus nigra. For three seedlings (4%), paternity was assigned to a cultivar of P. x canadensis. Almost two decades after reintroducing Populus nigra, the constitution of the seed and pollen pools changed in the study area in favour of reproduction of the native species and at the expense of the exotic poplar species. This study indicates that, although significant gene flow form exotic poplars is observed in European floodplains, restoration programmes of the native Populus nigra can vigorously outcompete the exotic gene flows and strongly reduce the impact of exotic Populus taxa on the softwood riparian forest development.

中文翻译：

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在恢复的洪泛区中重新引入本地黑杨，减少了外来杨树物种的传播

外来的胡杨类群对洪泛区的河岸森林恢复成功构成威胁。在引入原生的黑杨和重建自然河流动力学之后，我们评估了异域的胡杨类群对沿默兹河沿岸的软木河岸森林发展的影响。我们对154棵自发定居在恢复的生境中的杨树幼苗进行了采样，并根据诊断性叶绿体和核微卫星标记评估了它们的分类学。此外，通过对六种开放授粉的黑杨女性的72棵幼苗进行亲子关系分析，我们研究了经常种植的栽培杨与黑杨之间的自然杂交。分析的大部分来自砾石岸的杨树幼苗均鉴定为黑杨; 抽样的幼苗中只有2％表现出外来杨树种的基因。同样，来自开放授粉后代的大多数幼苗被鉴定为黑杨。对于三个苗（4％），侍被分配到的一个品种P. X黄花。再引入黑杨近二十年，种子和花粉池的组成在研究区域发生了变化，有利于本地物种的繁殖并以外来杨树物种为代价。这项研究表明，尽管在欧洲洪泛区中观察到了来自外来杨树的大量基因流，但天然黑杨的恢复计划可以大大胜过外来基因流，并极大地减少了外来杨树类群对软木河岸森林发展的影响。